Concerns about the security of oil supplies and the environmental consequences of burning fossil fuels have transformed the idea of a hydrogen (H2) economy from science fiction into a political bipartisan vision of our energy future. The challenge is now one of economics and technology. In one context, we already have a rapidly growing H2 economy, driven by the need for increased supplies of H2 to convert more abundant lower-grade crude oils into clean liquid fuels. This development is creating the infrastructure for a global H2 economy and provides powerful incentives to develop better methods of H2 production. The H2 content of liquid fuels is a variable; thus, there is also the option to add additional H2 to conventional liquid fuels to create H2-enhanced fuels. This option increases the liquid fuel yield per barrel of oil, creates a greatly expanded H2 production infrastructure, and may provide the easiest transition to a full H2 economy. It is primarily the characteristics of H2 as a fuel, rather than the type of device in which it is used (fuel cell or internal combustion engine), that creates the environmental benefits of a H2-fueled economy at the point at which the device is used. Water is the only waste product of H2 fuel. The other potential benefits of a H2 economy require methods of production that do not depend upon foreign energy resources and greatly reduce emission of greenhouse gases to the environment. Consequently, the most important challenges are the development of better methods to produce H2 and to store (deliver) H2 onboard vehicles. While fuel cells are not required for a revolution in transportation (internal combustion engines can burn H2), they add another dimension to the H2 economy by their potential impacts on electricity production and distribution. Hydrogen fuel cells may provide a storable form of electricity to meet peak electric demands. This benefits high-capital-cost low-production-cost energy sources such as nuclear and renewables by providing a demand for their energy output that is not tied to the daily cycle of electricity demand. The methods to produce and store H2 define the technical challenges. These challenges, in turn, define the challenges in heat transferâ??the subject of this Rohsenow Symposium. The likely characteristics of our transition to a H2 economy and some of the accompanying technical challenges in heat transfer are described herein.